The available data of AAV vectors in the clinic emphasize the importance of continued optimization efforts at the levels of the AAV capsid, genome and transgenic cassette. A focus of this proposal is to derive clinical AAV vector best suited for systemic disorders (MPS, Hurlers, etc.). At the capsid level, it is apparent that animal models do not always predict the human outcome and that more efficient human specific capsids are required to achieve a lower administered dose. In Aim 1, we seek to create a new paradigm of AAV vector selection for human transduction by generating the first AAV receptor expression map on tissues of mouse, primate and human origin. This tissue specific AAV receptor Atlas will be overlaid with AAV binding and transduction data in an effort to tease out regions of the capsid important for tissue specific interactions in varied backgrounds. In addition novel chimeric capsids isolated from a directed evolution strategy on primate and human livers established in a mouse model will be triaged against our receptor/binding atlas to determine if in vitro binding correlates to in vivo results. Then, capsid isolates from a primatized-liver mouse model will be investigated for primate liver transduction in vivo to determine if this strategy represents a valid method to derive primate (human & non human) liver specific AAV capsids. At the level of the AAV genome, we have assembled a panel of DNA repair dependent AAV substrates that report critical aspects of genome persistence including circularization, concatemerization and homology directed annealing. Investigations of these reagents in mutant backgrounds defective in different DNA repair pathways will offer insights into the preferred reliance on homologous recombination and non-homologous end joining mechanisms in vitro and in vivo providing a better prediction of vector performance in diseased settings (Aim 2). At the level of the vector transgene, we demonstrate in mouse liver, heart and eye a novel method to induce transgene synthesis using the IVS2- 654 intron and an anti-sense oligonucleotide. The work herein seeks to generate smaller synthetic variants that exhibit tighter control as well as altered transgene expression levels, thus providing a panel of regulatory switches which can be tailored for specific applications. Finally, a strategy is proposed to engineer an off switch for the induced transgene synthesis from IVS2-654, which may also allow the precise tuning of transgene synthesis at a fixed vector dose. Collectively, the results of the proposed experiments seek to address the observed clinical deficiencies in AAV gene therapy applications for diseases of systemic nature by our continued optimization efforts at the levels of the capsid and genome as well as the transgenic DNA cassette.